An example of the conventional pressure-sensitive sensors for measuring the pressure distribution of the external force applied to a selected surface is disclosed in Patent Document 1. As shown in FIG. 1 of Patent Document 1, this pressure-sensitive sensor comprises two films layered one above the other, an upper electrode provided in the top layer, a lower electrode provided in the bottom layer, and a pressure-sensitive ink layer disposed between the two layers.
When pressure is applied to the top-side film, only the portion receiving the pressure is made conductive in a vertical direction. Thus, an output is given only on part of the lower electrode corresponding to the portion receiving the pressure, thereby detecting the pressure distribution. This pressure-sensitive sensor may be provided inside of a vehicle seat, for example, to determine whether or not a person is present on the seat and also determine a physical build of the person based on the pressure distribution.
In other words, the pressure-sensitive sensor according to Patent Document 1 is configured to bring both the electrodes into contact with each other through the pressure-sensitive ink layer when pressure is applied, and to measure the pressure based on variations in resistance value in response to the pressure applied to the pressure-sensitive ink layer.
The applicant of the present invention also filed an application for a pressure-sensitive sensor comprising a pair of electrodes mounted on a bottom-side film in which the pair of electrodes are coated with pressure-sensitive conductive layer ink formed on a top-side film. This pressure-sensitive sensor dispenses with a spacer for an air layer because the pair of electrodes are mounted on the bottom-side film and normally coated with the pressure-sensitive conductive layer ink formed on the top-side film. Therefore, this sensor may assume any desired shape depending on how the electrodes are mounted. Further, the pair of electrodes are arranged frame-wise to provide a transparent central portion in the pressure-sensitive sensor, which allows a touch panel to be arranged in the transparent portion.